Solar hot water systems use various collectors or panels exposed to sunlight to accumulate heat energy in a working fluid circulated through the collector or panel. Some solar hot water systems circulate fresh water through the collector or panel in temperate climates where freezing temperatures are unusual. Freeze protection valves are employed in fresh water solar systems to prevent freeze damage to the collectors. Conservation of fresh water resources is important wherever such systems are used, so limiting the amount of flow necessary to prevent freeze damage to a minimum is a priority.
Depending on solar hot water system design and operating conditions, temperatures in the collector or panel can exceed the boiling point of water and produce potentially damaging pressures in the system. This can occur whenever water is not circulating in a collector exposed to hot sun. Typical solar hot water systems include a pressure relief valve to bleed off pressure in excess of a predetermined amount to prevent system damage. The pressure relief valve is separate from and in addition to the freeze protection valve.
The use of wax-filled actuators, otherwise referred to as wax motors, as thermally actuated control devices in fluid circulation systems is well known. Wax motors have been employed as actuators for valves employed to prevent fluid sources from freezing when the temperature drops. Such valves are designed to open or close in response to a predetermined change in temperature. Wax motors require no external power source, are reliable, extremely compact and powerful for their size.
Wax motors typically include a housing having a chamber filled with thermally responsive wax contained beneath a flexible diaphragm. The wax expands as temperature increases, exerting force on the diaphragm and on a reciprocating piston disposed on the other side of the diaphragm. Movement of the piston is controlled by a guide extending from the actuator housing. The wax motor is constructed such that known changes in temperature produce predetermined axial movement of the piston with respect to the housing.
Wax motor-actuated freeze protection valves are known where the piston is seated against a stop and the housing moves in response to changes in temperature. The housing carries a poppet that fits in a seat to control fluid flow. A return spring biases the housing and poppet away from the seat. At temperatures above freezing, the actuator exerts a force on the piston which moves the housing and poppet toward the seat against the bias of the return spring. At a predetermined temperature, typically above approximately 35° F., the force generated by the wax motor overcomes that of the return spring so that the poppet reaches the seat and the system is closed.
The intensity of the force generated by the wax motor changes with temperature, causing the actuator housing and poppet to move with respect to the valve seat at temperatures well above freezing. In freeze protection valves, the poppet must remain in the closed position over a wide range of greater than freezing temperatures while the actuator moves in response to temperature changes. Known valves of this type incorporate a poppet sub-assembly which accommodates actuator movement while maintaining the poppet in contact with the seat. The poppet sub-assembly includes a poppet retainer and poppet spring which allow the poppet to move independently of the actuator housing while the valve is closed. The retainer limits movement of the poppet toward the seat and the poppet spring defines the pressure exerted by the poppet on the seat. Thus, the poppet and seat remain stationary and sealed while the actuator housing moves in response to changes in temperature. The necessity for a poppet sub-assembly complicates both valve assembly and operation.
Consequently, there exists a need for a wax motor-actuated freeze protection valve that employs a simplified mechanism to remain closed over a range of temperatures.
There is also a need for a simple and reliable freeze protection valve that accurately opens to prevent freezing, while minimizing leakage at near freezing temperatures to reduce waste of water.